In recent years, magnetoresistive random access memories using a tunneling magnetoresistive effect have been proposed. In this type of memory, an MTJ (Magnetic Tunnel Junction) element having a multilayer of a metal magnetic film/insulation film/metal magnetic film is used. The variation in resistance of the MTJ element is determined by the magnetic states of metal magnetic bodies on both interfaces of an insulation film, and data is stored by the magnetization state of the MTJ element.
As methods of varying the magnetization state of the MTJ element, there are a “current field write method” using a magnetic field which is generated by an electric current through wiring lines, and a “spin transfer torque writing method” using a spin-polarized electric current. In the current field write method, since it is necessary to dispose wiring lines for generating a magnetic field in the vicinity of the MTJ element, there is a problem that an increase in integration is difficult. On the other hand, in the spin transfer torque writing method, since a memory cell is basically composed of a pair of cell select transistors and an MTJ element, like a DRAM, there is a feature that an increase in integration is easy.
However, in the spin transfer torque writing method, although the magnetic state is controlled by the direction of a current flowing in the MTJ element, a relatively high current density (˜1 MA/cm2) is necessary at the time of write. Hence, a select transistor, which enables the flow of a current corresponding to the area of the MTJ element, is required, leading to a bottleneck to the reduction in size of the select transistor.
If the volume of the magnetic body which constitutes the MTJ element is small, the write current can be decreased and the current flowing in the select transistor can be reduced. However, if the film thickness of the magnetic body is decreased, the magnetic anisotropy energy decreases, and this causes degradation in retention or a decrease in signal amount. In addition, since the area of the MTJ element is determined by the minimum feature dimension of lithography, there is a problem that it is difficult to reduce the volume of the magnetic body.